Such an assembly is known, for example, from German published specification No. 2,138,966 or U.S. Pat. No. 3,199,901. The ducts here considered are normally made of light-gauge galvanized sheet steel having little inherent structural strength so that the provision of a reinforcing joint assembly is essential for a good connection to an adjoining duct or other support.
Such a joint assembly normally is composed of a plurality of profiles, one for each sidewall of the duct, and as many corner pieces each interlinking two adjacent profiles to form a closed polygonal structure or frame. Normally the profiles at least are made of rolled inexpensive sheet metal. The difficulty with such systems is that the production of the profiles by rolling as well as the conditions of use often generate stresses resulting in an excessive deformation of the profiles so that leekproofness of the joint is no longer assured.